Influence of epitaxial mounds on the yield of integrated circuits

As the structural and functional complexities in integrated circuits increase, yield prediction becomes as important as the calculation of electrical characteristics. This paper analyzes the yield loss resulting from the presence of the epitaxial mound, a material defect found very frequently on the epitaxial surface. The peculiarity of this yield-loss mechanism, especially in a contact printing system, is that not only does it act as a crystallographic imperfection but its damage accumulates on the emulsion or chromium photomask and thus propagates to other slices. Statistical investigations on its behavior have shown that the latter effect can be more detrimental than the former in large scale integration. These results are summarized in a simple mathematical expression that is used for yield prediction. Using the model, the damage by the epitaxial mound has been shown to be reduced by an improvement in photoetching process management, though the ideal solution lies in the reduction of the mound itself or in the use of a noncontact printing system.